BACKGROUND: The diagnosis of Cushing disease is based on endocrinological parameters, with no single test being specific. In some patients, dynamic thin-slice sellar magnetic resonance imaging fails to detect a pituitary tumor.

OBJECTIVE: The purpose of this study is to investigate the role of ectopic pituitary adenoma in this situation.

RESULTS: In all 5 patients (all female, 32-41 years of age), an exclusively extrasellar ACTH-secreting adenoma was excised. Three adenomas were located in the cavernous sinus, 1 in the sphenoid sinus, and 1 in the ethmoidal cells. Histologically, none of the tumors showed signs of aggressiveness. Three of the 5 adenomas specifically expressed somatostatin receptor 5. In 4 patients with Cushing disease, postoperative remission was obtained, with 1 recurrence after 14 months. In the patient with Nelson syndrome, ACTH decreased from >800 to <80 pg/mL. Three patients underwent previous surgery elsewhere, including 1 hypophysectomy. In this case, the ectopic adenoma (positive for somatostatin receptor 5) in the ethmoidal cells turned out to be positive on gallium 68 DOTATATE positron emission tomography/computed tomography.

CONCLUSIONS: The incidence of primarily ectopic ACTH-secreting adenomas in this series was 6%. In cases of negative MRI findings, an ectopic ACTH-secreting adenoma should be taken into account. 68Ga DOTATATE positron emission tomography/computed tomography may identify ectopic pituitary adenomas. Hypophysectomy should always be avoided in primary surgery for CD.